Conventional personnel computer (PC) or other electronic equipment usually has a power management and control apparatus for power saving. Conventional power supply unit has two converters, one is used for main power and the other, the smaller one, is used for standby power. The power management and control apparatus is powered by the standby power. When PC or other electronic equipment operates, the power supply unit provides main power. When the system is in standby status, the main power of the power supply unit will be shut down. Only standby power is provided for the power management and control apparatus.
Conventional power supply unit further has protection circuit device to provide protection function when a failure (such as over-voltage, over-current, under-voltage, over-power) occurs. There are two types of protection circuit, latch and non-latch. A latch type protection circuit can latch the protection circuit and shut down the power when a failure occurs. After the failure is repaired, the power needs to be restarted to recover since the power will not be recovered automatically. A non-latch type protection circuit can activate the protection function and stop providing power when a failure occurs. After the failure is repaired, the power will be provided automatically.
Although the latch type protection circuit can provide reliable protection for the components of the power supply unit, the supply of the power can not be recovered automatically when the failure is repaired once the protection function is activated. An additional procedure to restart the power is required to recover the power. Further, when manufacturing the power supply unit with latch type protection circuit used for such as PC, the power needs to be turned on and off for testing if the protection function is operated normally, which is time-consuming.
In order to overcome the above defects of latch type protection circuit, one conventional technology provides an additional time-delay circuit. That conventional technology uses the time-delay circuit to delay the shutdown control signal when the protection circuit latch is going to be occurred due to an AC interruption or a removal of the input voltage, to avoid the latch action in this situation. However, the additional delay time is still time-consuming. Therefore, what is needed is a simpler and more economic power supply unit protection circuit device.